This invention relates to a method for the preparation of polymeric particles suitable for use as electrostatographic toner, and more particularly, to a method for the preparation of toner particles of controlled shape in which flocculating agents are employed for controlling morphology of the toner particles.
Electrostatic toner polymer particles can be prepared by a process frequently referred to as xe2x80x9climited coalescencexe2x80x9d. In this process, polymer particles having a narrow size distribution are obtained by forming a solution of a polymer in a solvent that is immiscible with water, dispersing the solution so formed in an aqueous medium containing a solid colloidal stabilizer and removing the solvent by evaporation. The resultant particles are then isolated, washed and dried.
In the practice of this technique, toner particles are prepared from any type of polymer that is soluble in a solvent that is immiscible with water. Thus, the size and size distribution of the resulting particles can be predetermined and controlled by the relative quantities of the particular polymer employed, the solvent, the quantity and size of the water insoluble solid particulate suspension stabilizer, typically silica or latex, and the size to which the solvent-polymer droplets are reduced by agitation.
Limited coalescence techniques of this type have been described in numerous patents pertaining to the preparation of electrostatic toner particles because such techniques typically result in the formation of toner particles having a substantially uniform size distribution. Representative limited coalescence processes employed in toner preparation are described in U.S. Pat. Nos. 4,833,060 and 4,965,131 to Nair et al.
U.S. Pat. No. 5,283,151 is representative of earlier work in this field and describes the use of carnauba wax to achieve similar toner morphology. The method comprises the steps of dissolving carnauba wax in ethyl acetate heated to a temperature of at least 75xc2x0 C. and cooling the solution, so resulting in the precipitation of the wax in the form of very fine needles a few microns in length; recovering the wax needles and mixing them with a polymer material, a solvent and optionally a pigment and a charge control agent to form an organic phase; dispersing the organic phase in an aqueous phase comprising a particulate stabilizer and homogenizing the mixture; evaporating the solvent and washing and drying the resultant product.
Unfortunately, this technique requires the use of elevated temperature to dissolve the wax in the solvent and cooling the solution to precipitate the wax. The wax does not stay in solution of ethyl acetate at ambient temperature and as a result it is very difficult to scale up using this methodology.
The shapes of the toner particles have a bearing on the electrostatic toner transfer and cleaning properties. Thus, for example, the transfer and cleaning efficiency of toner particles have been found to improve as the sphericity of the particles are reduced. Thus far, workers in the art have long sought to modify the shape of the evaporative limited coalescence type toner particles by means other than the choice of pigment, binder, or charge agent. The shape of the toner particles are modified to enhance the cleaning and transfer properties of the toner.
In accordance with the present invention, the prior art limitations are effectively obviated by a novel process in which specified flocculating agents are introduced into the aqueous phase of the limited coalescence process. The use of the flocculating agents result in the formation of non-spherical toner particles after the solvent is removed. The toner morphology is controlled independently of the toner composition (i.e. resin, binder matrix, pigment, charge control agent, etc.). The degree of non-sphericity is directly related to the concentration of flocculating agent.
Thus, viewed from one aspect, the present invention is directed to a method for the preparation of electrostatographic toner comprising the steps of:
a) dissolving a polymer material and optionally a pigment and a charge control agent in an organic solvent to form an organic phase;
b) dispersing the organic phase in an aqueous phase comprising a particulate stabilizer and optionally a promoter to form a dispersion and homogenizing the resultant dispersion wherein a flocculating agent is added to the aqueous phase either before or after homogenation;
c) evaporating the organic solvent and recovering a resultant product; and
d) washing and drying the resultant product.
Viewed from another aspect, the present invention is directed to a process for preparing electrophotographic toner by dispersing an organic phase in an aqueous phase to yield a layer of particulate suspension stabilizer on the surface of the polymer. The improvement in the process comprises adding the flocculating agent, particulate stabilizer and promoter to the aqueous phase in the aforementioned limited coalescence process.
It is an advantage of the present invention that elevated temperatures are not needed. It is also an advantage that the flocculating agents are water soluble or water dispersible and so it is relatively easy to scale up production.
These and other features and advantages of the present invention will be better understood taken in conjunction with the following detailed description and claims.
In accordance with the present invention, a pigment dispersion is prepared by conventional techniques as, for example, by media milling, melt dispersion and the like. The pigment dispersion, polymer material, a solvent and optionally a charge control agent are combined to form an organic phase. This mixture is permitted to stir overnight and then dispersed in an aqueous phase comprising a particulate stabilizer and optionally a promoter.
The resultant mixture is then subjected to mixing and homogenization. The flocculating agent is added to the aqueous phase either before or after mixing/homogenization. In this process, the particulate stabilizer forms an interface between the organic globules in the organic phase. Due to the high surface area associated with small particles, the coverage by the particulate stabilizer is not complete. Coalescence continues until the surface is completely covered by particulate stabilizer. Thereafter, no further growth of the particles occurs. Accordingly, the amount of the particulate stabilizer is inversely proportional to the size of the toner obtained. The relationship between the aqueous phase and the organic phase, by volume may range from 1:1 to approximately 9:1. This indicates that the organic phase is typically present in an amount from about 10% to 50% of the total homogenized volume.
Following the homogenization treatment, the solvent present is removed by evaporation or boiling, optionally under vacuum, and the resultant product washed and dried.
The solvents chosen for use in the organic phase steps may be selected from among any of the well-known solvents capable of dissolving polymers. Typical of the solvents chosen for this purpose are chloromethane, dichloromethane, ethyl acetate, vinyl chloride, n-propyl acetate, iso-propyl acetate, trichloromethane, carbon tetrachloride, ethylene chloride, trichloroethane, toluene, xylene, cyclohexanone, 2-nitropropane and the like.
The particulate stabilizer selected for use herein may be selected from among highly cross-linked polymeric latex materials of the type described in U.S. Pat. No. 4,965,131 to Nair et al., or silicon dioxide. Silicon dioxide is preferred. It is generally used in an amount ranging from 1 to 15 parts, by weight, based on 100 parts of the total solids in the toner. The size and concentration of these stabilizers control and predetermine the size of the final toner particles. In other words, the smaller the size and/or the higher the concentration of such particles, the smaller the size of the final toner particles.
Any suitable promoter that is water soluble and affects the hydrophilic/hydrophobic balance of the solid dispersing agent in the aqueous solution may be employed in order to drive the solid dispersing agent, that is, the particulate stabilizer, to the polymer/solvent droplet-water interface. Typical of such promoters are sulfonated polystyrenes, alginates, carboxy methylcellulose, tetramethyl ammonium hydroxide or chloride, diethylaminoethylmethacrylate, water-soluble complex resinous amine condensation products of ethylene oxide, urea and formaldehyde and polyethyleneimine. Also effective for this purpose are gelatin, casein, albumin, gluten and the like or non-ionic materials such as methoxycellulose. The promoter is generally used in an amount from about 0.2 to about 0.6 parts per 100 parts of aqueous solution by weight.
Various additives generally present in electrostatographic toner may be added to the polymer prior to dissolution in the solvent or in the dissolution step itself, such as charge control agents, waxes and lubricants. Suitable charge control agents are disclosed, for example, in U.S. Pat. Nos. 3,893,935 and 4,323,634 to Jadwin et al., U.S. Pat. No. 4,079,014 to Burness et al. and British Patent No. 1,420,839 to Eastman Kodak. Charge control agents are generally employed in small quantities such as from about 0 to 10 parts per hundred based upon the weight of the total solids content (weight of the toner) and preferably from about 0.2 to about 3.0 parts per hundred.
As indicated, the present invention is applicable to the preparation of polymeric toner particles from any type of polymer that is capable of being dissolved in a solvent that is immiscible with water and includes compositions such as, for example, olefin homopolymers and copolymers, such as, polyethylene, polypropylene, polyisobutylene and polyisopentylene; polytrifluoroolefins; polytetrafluoroethylene and polytrifluorochloroethylene; polyamides, such as polyhexamethylene adipamide, polyhexamethylene sebacamide, and polycaprolactam; acrylic resins, such as polymethylmethacrylate, polymethylacrylate, polyethylmethacrylate and styrene-methylmethacrylate; ethylene-methylacrylate copolymers, ethylene-ethyl acrylate copolymers, ethylene-ethyl methacrylate copolymers, polystyrene and copolymers of styrene with unsaturated monomers such as butyl acrylate-styrene copolymer, cellulose derivatives, polyesters, polyvinyl resins and ethylene-vinyl alcohol copolymers and the like. Preferably, the polymer material is polyester or butyl acrylate-styrene copolymer.
Pigments suitable for use in the practice of the present invention should be capable of being dispersed in the polymer, insoluble in water and yield strong permanent color. Typical of such pigments are the organic pigments such as phthalocyanines, lithols and the like and inorganic pigments such as TiO2, carbon black and the like. Typical of the phthalocyanine pigments are copper phthalocyanine, a mono-chloro copper phthalocyanine, and hexadecachloro copper phthalocyanine. Other organic pigments suitable for use herein include anthraquinone vat pigments such as vat yellow 6GLCL1127, quinone yellow 18-1, indanthrone CL1106, pyranthrone CL1096, brominated pyranthrones such as dibromopyranthrone, vat brilliant orange RK, anthramide brown CL1151, dibenzanthrone green CL1101, flavanthrone yellow CL1118; azo pigments such as toluidine red C169 and hansa yellow; and metallized pigments such as azo yellow and permanent red. The carbon black may be any of the known types such as channel black, furnace black, acetylene black, thermal black, lamp black and aniline black. The pigments are employed in an amount sufficient to give a content thereof in the toner from about 1% to 40%, by weight, based upon the weight of the toner, and preferably within the range of 4% to 20%, by weight.
Flocculating agents are listed in detail in the book xe2x80x9cThe Chemistry of Silicaxe2x80x9d by R. K. Iler (John Wiley and Sons, 1979, pp.384-396). Preferred flocculating agents suitable for use in the present invention include cationic surfactants, basic metal salts, cationic polymers and inorganic colloids. The flocculating agent may comprise 0.0001-50% by weight of the total solids present in the organic phase.
Preferred cationic surfactants are ammonium salts having the general form, 
where X may be H2PO4, OH, Br or Cl, each R1 may be individually selected from the form xe2x80x94(CH2)nY, where Y may be either 
xe2x80x94OH or xe2x80x94H, and R2 has the form xe2x80x94(CH2)pZ, where Z may be xe2x80x94H or xe2x80x94NHOOC(CH2)pCH3, each n may be individually selected from the integers ranging from 0 to 5, and each p may be individually selected from the integers ranging from 0 to 20. Typical of such materials are dodecyl ammonium chloride and octadecyl trimethyl ammonium bromide and long chain betaines like dodecyl betaine.
Additional preferred cationic surfactants are long chain pyridinium salts, wherein long chain is a hydrocarbon with 8 or more carbons in it, such as cetyl pyridinium bromide.
Additional preferred cationic surfactants are ammonium salts having the general form, Rxe2x80x94(Oxe2x80x94CH(CH3)xe2x80x94CH2)nxe2x80x94Oxe2x80x94R, where each R is individually selected from xe2x80x94CH2xe2x80x94CH(N+(R1)3)xe2x80x94CH3 Xxe2x88x92 or xe2x80x94CH2xe2x80x94CH2xe2x80x94Oxe2x80x94CH3, but at least one of R is xe2x80x94CH2xe2x80x94CH (N+(R1)3)xe2x80x94CH3 Xxe2x88x92, where each R1 may be individually selected from xe2x80x94H or xe2x80x94(CH2)mxe2x80x94CH3 where m is selected from integers 0 to 3 and X is elected from H2PO4, Cl or Br, where n is selected from integers 3 to 50.
Additional preferred cationic surfactants are ammonium salts having the general form:
Rxe2x80x94(Oxe2x80x94CH(CH3)xe2x80x94CH2)nxe2x80x94(Oxe2x80x94CH2xe2x80x94CH2)mxe2x80x94(Oxe2x80x94CH(CH3)xe2x80x94CH2)nxe2x80x94Oxe2x80x94R,
where each R is individually selected from xe2x80x94CH2xe2x80x94CH (N+(R1)3)xe2x80x94CH3 Xxe2x88x92 or xe2x80x94CH2xe2x80x94CH2xe2x80x94Oxe2x80x94CH3, but at least one of R is xe2x80x94CH2xe2x80x94CH (N+(R1)3)xe2x80x94CH3 Xxe2x88x92, where each R1 may be individually selected from xe2x80x94H or xe2x80x94(CH2)pxe2x80x94CH3 where p is selected from integers 0 to 3 and X is elected from H2PO4, Cl or Br, where each n and m are individually selected from integers 2-30.
Preferred basic metal salts are aluminum salts such as aluminum chloride, aluminum acetate, aluminum acetylacetonate.
Additional preferred basic metal salts are gallium(III) salts such as gallium(III) bromide and gallium(III) chloride, gallium(III) acetylacetonate.
Preferred cationic polymers are homopolymers or (meth)acrylates copolymers of quaternary ammonium substituted (meth)acrylates such as poly(meth)acrylyloxyethyldiethylmethylammonium Bromide.
Additional preferred cationic polymers are polyvinylpyridinium salts such as poly(2-methyl-5-vinylpyridium halide) and ply(N-methyl-4-vinylpyridinium bromide).
Additional preferred cationic polymers are copolymers of acrylamide and a cationic monomer like N-phenyl-2-vinylpyridinium bromide.
Additional preferred cationic polymers are cationic linear or branched polyethyleneimine at pH  less than 6.
Additional preferred cationic polymers are the products of the condensation polymerization between one or more dicarboxylic acids and an aminoalcohol, diamine, or diol, wherein at least one of the groups contained in one of the organic dicarboxylic acid chains carries a positive charge. Such cationic polymers have the general form, 
where R1 may be (CH2)n or 
R2 is phenylmethylphosphonium 4,4xe2x80x2-benzamide p-toluenesulfonate or triphenylmethylphosphonium p-toluenesulfonate, R3 may be chosen from the following: 
xe2x80x94O(CH2)nO(CH2)nOxe2x80x94,
or 
where each n may be independently selected from the integers ranging from 1 to 8, each p may be independently chosen from the integers ranging from 0 to 5, and a ranges from 0.00-0.99.
Preferred inorganic colloids are colloidal alumina and any colloidal silica with opposite charge of colloidal silica used as a stabilizer in the present invention such as positively charged LUDOX CL(copyright) silica or negatively charged NALCOAG 1060(copyright) silica.
A spherical particle is well known and is defined as a three dimensional object which has all points on the surface essentially equidistant from a central point. By non-spherical particle is meant a three dimensional object in which individual points on the surface have varying distances from a central point. This will be seen as irregular, or oblong, or wrinkled shapes and surfaces.